Heat strippable coating composition and a metal article coated therewith



Dec. 6, 1949 [ATT 2,490,752

G HEAT STRIPPABLE CO NG COMP TION AND METAL ARTICLES COATED TH WITHFiled June 2'7, 1946 50 v sol Gordon D. f/fazz INVENTOR Patented Dec. 6,1949 UNITED STATES i EtTENT OFFlfiE HEAT STRIPPABLE COATING COMPOSITIONAND A METAL ARTICLE COATED THERE- WITH Application June 27, 1946, SerialNo. 679,765

Claims.

This invention relates to a composition adapted to the coating of metalpieces to prevent rusting or other types of corrosion which compositionconsists of a partially hydrolyzed cellulose acetate butyrate of certaincharacteristics and at least an equal amount of an oil-like materialcontaining a substantial proportion of mineral oil, at least 30% of theoil-like material being castor oil, methyl abietate, or hydrogenatedmethyl abietate, or a mixture thereof. This invention also includes theapplication of that composition to metal articles and the articlesprotected by a coating of this composition.

In the transporting of metal parts, particularly of iron of steel, thereis danger from rusting or other types of corrosion. This has beenparticularly true in recent years because much of this material was intransport for long periods of time and in many cases in regions ofunusual dampness and other adverse conditions. Formerly metal articleswere prevented from rusting by applying thereto a heavy grease Whichwould adhere to the article, thereby forming a coating thereon. Thispractice, however, had the disadvantages that the articles weredifiicult to handle and after arriving at the destination required theuse of a solvent to remove the grease therefrom. As a consequence,compositions have been developed which would form a coating on metalarticles which could be handled without coming off onto the hands andwhich could at the point of destination be stripped from the metalarticle making any cleaning operation unnecessary. As most coatings arenot completely moistureproof, it has been necessary for this purpose todevelop coatings which would form a protective covering for the metalthrough which no moisture would penetrate. Also, the coatingcompositions which have been used give coatings of comparatively poorstrength necessitating thick coatings such as in the order of magnitudeof A; inch.

One object of my invention is to provide a coating composition for metalarticles which can be readily handled but through which no moisture canpenetrate to the metal itself. Another object of my invention is toprovide a composition which forms a protective coating that may bereadily peeled oil from an article at the time of use. A further objectof my invention is to provide a cellulose ester composition which may beI applied as a melt to a rust-susceptible article by a dipping operationand upon cooling, a hard, transparent flexible surface is obtained. Astill further object of my invention is to provide a composition whichforms films of superior strength, thus making possible comparativelythin coatings. Other objects of my invention will appear herein.

I have found that articles susceptible to rust or corrosion are wellprotected by coating those articles with a melt consisting of acellulose acetate butyrate having certain prescribed characteristics andat least an equal amount of an oil-like material of which at least 30%is castor oil, alkyl abietate or hydrogenated alkyl abietate and 4-20%of the oil-like material is a mineral oil. This material is applied byheating the composition to a temperature of ISO-200 C. and thoroughlymixing the cellulose ester and oil like material together, whereupon thecomposition is applied as a layer on the metal part, such as by aclipping operation. Upon removal of the article from the melt, thecoating on the metal article solidifies forming a hard, transparent,flexible surface which prevents contact of the article with water, air,or other corrosive agents. The coating which is obtained may be readilypeeled from the article at any time.

It is a feature of my composition that it permits the slow exudation ofmineral oil or rustpreventive oil from the coating onto the metalarticle. This exudation results in a very thin oil coating directly onthe metal article underneath the protective coating thereon so that anymoisture vapor which should penetrate the outer coating will not reachthe metal surface. Polished mild steel plates to which had been appliedcoatings of my composition .1 inch thick were held in a closed containerfor 150 days under water at F. without showing any sign of rust.

Another feature of my composition is that the 'coatings thereof havegood strength and, therefore, the coatings which are applied to metalarticles may be comparatively thin and still constitute good protectionagainst handling. For instance, coatings within the range of .92 to 0.1inch are ordinarily quite suitable for adequately protecting a metalarticle although, if desired, coatings of greater thickness may beemployed. If the article coated has sharp projections, it is desirableto apply a preliminary coat to those projections prior to the generalcoating of the entire article.

The accompanying drawing is a triangular graph showing the region fromwhich the cellulose acetate butyrates must selected for use incompositions in accordance with my invention, these esters having theright compatibility and strength characteristics for use in myinvention. This triangular graph is made up of three points,

one of which is on the line designating butyryl and is at 57.2%, thepercentage of butyryl in a fully esterified cellulose butyrate. Thepoint on the line designating acetyl is at 44.9%, the percentage ofacetyl in a fully esterified cellulose acetate. Any point within thetriangle represents a cellulose ester of a certain acetyl and butyrylcontent, indicated by the location of the point in the triangle. Forinstance, the point where the 30% acetyl line initially intersects the Sin triester represents a cellulose acetate butyrate having an acetylcontent of 30% and a butyryl content of approximately 17%. Also, it maybe concluded that this is not a fully esterified ester as the point isnot on the triester line. These useful esters range from 45 to 52%combined butyryl and 1 to 9% acetyl and have a hydroxyl content rangingfrom 0.1 to 0.4 hydroxyl per glucose unit. The esters which are used inpreparing compositions of my invention must have a viscosity within therange of -150 centipoises as measured by their 10% solution in acetoneat C. Lower viscosity esters give coats of poor strength which arecharacterized by tearing, whereas esters having a high viscositynecessitate too high an operating temperature for practical Value.Cellulose esters suitable for use in preparing my compositions may beprepared by reacting upon cellulose with butyric anhydride, preferablyafter a pre-soaking or pretreatment with a small amount of acetic acid.For instance, by means of a pretreatment such as described and claimedin Malm Patents Nos. 2,342,415 and 2,342,416, the cellulose is activatedusing only a small amount of acetic acid. Esterification of thispretreated cellulose with butyric anhydride and catalyst, such as by themethod described and claimed in Blanchard Patent No. 2,304,792, or MalmPatents Nos. 2,362,576 and 2,345,406, results in a high butyrylcellulose ester, the butyryl and acetyl contents of the esterificationbath being adjusted so as to give a butyryl content within the range ofto 52%. The ester is then hydrolyzed to impart thereto a hydroxylcontent of 0.1 to 0.4 hydroxyl per glucose unit. If the esters are to besubjected to heat for a considerable time, it might be desirable to alsosubject those esters to a stabilization treatment, such as by the methoddescribed in Malm and Kirton Patent No. 2,250,201 or that described inMalm and Crane Patent No. 2,346,498. Whether or not stabilization of theester is desirable will depend on Whether or not any discoloration ofthe unstabilized ester takes place in the dipping operations and, if so,if the amount of discoloration is objectionable for the particularpurpose for which the coating is employed.

The oil-like material with which the cellulose ester is mixed may becastor oil, an alkyl abietate or a hydrogenated alkyl abietate, or maybe a mixture of these materials with themselves or with otherhigh-boiling esters, such as dibutyl sebacate, di-2-ethyl hexylphthalate, methoxy ethyl stearate, a chlorinated diphenyl known asArocolor, or some other plasticizer of high molecular weight. Inaccordance with my invention, however, the oil-like material should becomposed of at least 30% of castor oil, alkyl abietate, hydrogenatedalkyl abietate, or their mixture. This oil-like material contains inaccordance with my invention a proportion of mineral oil within therange of 4-20%. The mineral oil which is used is preferably a light oilcharacterized as a rustpreventive oil. However, any type of lightmineral oil, such as spindle oil, fuel oil Nos. 5 and 6 (bunker C oil)or lubricating oil may be employed as the mineral oil constitutent ofthe oillike material which is mixed with the cellulose ester to formcompositions in accordance with my invention. In view of the use towhich the composition is put, it is desirable that the oil employed havea boiling point of at least 200 C.

If an alkyl abietate is employed, it may be any one of methyl, ethyl,isopropyl, butyl, or amyl abietate. The most readily available alkylabietate is methyl abietate which is marketed under the trade nameAbalyn, preparation of this ester being described in U. S. Patent No.1,944,241 of Humphrey. Also, any of the hydrogenated alkyl abietates maybe employed. Hydrogenated methyl abietate is the most common of thesematerials, at the present time this material being marketed under thetrade name Hercolyn and described in U. S. Patent No. 1,944,241. If itis desirable to mix other materials with the castor oil or theabietates, we have found that a chlorinated diphenyl is very useful forthis purpose. Chlorinated diphenyls are marketed at the present timeunder the trade name Aroclor, those having low melting points asrepresented by Aroclors Nos. 4465 and 5442 being especially suitable asa diluent in preparing compositions for protective coating purposes. Itis desirable that the castor oil or the abietates or their mixture,however, constitute at least 30% of the oil-like material used.

I have found that the most useful compositions in accordance with myinvention consist of an amount of cellulose ester within the range of50-60%, the remainder being the oil-like material described herein. Withthe use of a cellulose ester within the range of 50-60% of the totalcomposition, a composition is obtained having good coating properties,and the resulting coating exhibits no tackiness after it has cooled.This composition is useful for coating metal gears, housings, valves,rods, assemblies of parts, or, in fact, any metal part which is to betransported before use. The coatings in accordance with my invention aretransparent and, hence, not only can the nature of the part enclosed bedetermined without stripping the coating therefrom, but any letteringwhich is present thereon may be observed. The preierred method ofcoating merely consists in forming a melt composition in accordance withmy invention at a temperature within the range of -200 C. and dippingthe clean metal part therein. The thickness or the coating which is tobe applied may be adjusted by the viscosity of the bath in which thepart is dipped. This viscosity may be adjusted by the viscosity of theester which is used, or by the temperature to which the melt is heated.If desired, a small proportion, such as 1% of an antioxidant, such ashydroquinone, may be incorporated in the molten mass.

The following examples illustrate my invention:

Example 1.A composition was prepared by mixing together 55 parts of acellulose acetate butyrate having a butyryl content of 47%, an acetylcontent of 6.5%, and approximately .2 hydroxyl per glucose unit, and aviscosity of 25 centipoises with 40 parts of hydrogenated methylabietate and 5 parts of a rust-preventive mineral oil. At C. the masswas found to form a clear homogeneous melt, and this bath was used as adipping bath to apply protective coatings on the surface of metal parts.

Example 2.A mixture of 60 parts of cellulose acetate butyrate of asimilar type to that used in the preceding example was mixed with 38parts of castor oil and 2 parts of mineral lubricating oil and washeated to 160 C. to give a smooth solution. Clean steel plates suspendedby a wire were dipped into this solution and then allowed to drain andcool. The plates were protected against corrosion by this covering.

Example 3.Fifty-five parts of cellulose acetate butyrate of the typedescribed above were mixed with 35 parts of methyl abietate and parts ofa rust-preventive mineral oil. The mixture was heated to 180 0., thencooled to 150 C. for dipping. Metal pieces were dipped, and the coatingwas found to set quickly after removal from the clipping bath.

Example 4.A composition was prepared consisting of 50 parts of celluloseacetate butyrate of the type prescribed herein, parts of castor oil, 10parts of hydrogenated methyl abietate, 15 parts of Aroclor No. 5460, and5 parts of rustpreventive mineral oil. The composition was meltedtogether and a clean steel plate was dipped therein. Upon cooling andsetting, a good protective coating resulted, the coating having atensile strength of 351 pounds per square inch.

Example 5.A composition was prepared consisting of 50 parts of celluloseacetate butyrate, 30 parts of Hercolyn, 15 parts of Aroclor No. 5460,and 5 parts of mineral oil. A clean steel plate was dipped at 190 C.resulting in a clear coating thereon having a thickness of .077 inch.The resulting coating had a tensile strength of 372 pounds per squareinch.

I claim:

1. A heat strippable protective coating composition essentiallyconsisting of 50-60% of a cellulose acetate butyrate having a butyrylcontent of 45-52%, an acetyl content of 1-9%, 01-04 hydroxyl per glucoseunit and a viscosity within the range of 15-150 centipoises and 40-50%of an oillike material essentially consisting of 4-20% of mineral oil,at least 30% of a chlorinated diphenyl and at least 30% of an esterselected from the group consisting of the lower alkyl abietates and thehydrogenated lower alkyl abietates.

2. A heat strippable protective coating composition essentiallyconsisting of 50-60% of a cellulose acetate butyrate having a butyrylcon- 6 tent of 45-52%, an acetyl content of 1-9% 0.1-0.4 hydroxyl perglucose unit and a viscosity within the range of 15-150 centipoises and40-50% of an oil-like material essentially consisting of 4-20% ofmineral oil, at least 30% of a chlorinated diphenyl and at least 30% ofa methyl abietate.

3. A heat strippable protective coating composition essentiallyconsisting of 50-60% of a cellulose acetate butyrate having a butyrylcontent of 45-52%, an acetyl content of 1-9%, 0.1-0.4 hydroxyl perglucose unit and a viscosity within the range of 15-150 centipoises and40-50% of an oillike material essentially consisting of 4-20% of mineraloil, at least 30 of a chlorinated diphenyl and at least 30% of ahydrogenated methyl abietate.

4. A heat strippable protective coating composition essentiallyconsisting of of a cellulose acetate butyrate having a butyryl contentof 45-52%, an acetyl content of 1-9%, 0.1-0.4 hydroxyl per glucose unitand a viscosity within the range of 15-150 centipoises, 30% ofhydrogenated methyl abietate, 15% of chlorinated diphenyl, and 5% ofmineral oil.

5. A metal article which is subject to corrosion having a strippableoil-exuding coating thereon consisting of 50-60% of a cellulose acetatebutyrate having a butyryl content of 45-52%, an acetyl content of 1-9%,0.1-0.4 hydroxyl per glucose unit and a viscosity within the range of15- centipoises, and 40-50% of an oil-like material containing 4-20% ofmineral oil, at least 30% of a chlorinated diphenyl and at least 30% ofhydrogenated methyl abietate.

GORDON D. HIATT.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,877,179 Humphrey Sept. 13, 19321,999,812 Humphrey Apr. 30, 1935 2,216,827 Mitchell Oct. 3, 19402,272,706 Harnett Feb. 10, 1942 2,372,982 Richards et a1 Apr. 3, 19452,385,377 Opp Sept. 25, 1945 2,394,101 Phillips Feb. 5, 1946 2,409,989Salo Oct. 22, 1946

